Combining cefoperazone, piperacillin or ticarcillin with the beta-lactamase inhibitors sulbactam, tazobactam or clavulanic acid, respectively, results in compounds with activity against a wide range of Gram-positive and Gram-negative aerobic and anaerobic organisms, including strains producing beta-lactamases. Pharmacokinetics of the three combinations are similar. Cefoperazone/sulbactam can be given twice daily as opposed to a minimum of three-times-daily dosing required with the other combinations. All 9 combinations have a good safety profile, and may be administered parenterally for the treatment of severe infections in hospitalized patients, including intra-abdominal, gynaecological, skin and soft tissue infections. Additional cover may be provided by administering one of these combinations with an aminoglycoside.